This invention relates generally to accessing objects in a stack of objects for removal and, more particularly, to an apparatus for randomly accessing a magnetic tape cartridge from a stack of magnetic tape cartridges to efficiently load and unload magnetic tape cartridges on a tape drive.
In the past, an operator manually loaded and unloaded magnetic tape cartridges of the IBM 3480 type into a tape drive one magnetic tape cartridge at a time. The tape drive ejected the magnetic tape cartridge once the associated data processing system read/wrote data on the magnetic tape. The tape drive remained in an idle state until an operator retrieved the magnetic tape cartridge ejected by the tape drive and replaced it with a new magnetic tape cartridge. Such a manual operation was time consuming, inefficient and prone to error.
An improvement over this manual magnetic tape cartridge loading arrangement was the use of an automatic loader mechanism which typically consisted of a plurality of individual tape cartridges storage slots, each of which held a single 3480 type magnetic tape cartridge. An operator manually loaded each magnetic tape cartridge, one at a time, into a corresponding individual magnetic tape cartridge storage slot of this automatic loader mechanism.
The automatic loader mechanism sequentially and automatically loaded each of the magnetic tape cartridges into the tape drive associated with the automatic loader mechanism. This was accomplished by sequentially translating the magnetic tape cartridge "rack", one individual magnetic tape cartridge storage slot at a time, into position in front of the tape drive. The magnetic tape cartridge stored in the corresponding individual magnetic tape cartridge storage slot was then loaded into the tape drive. Once the loaded magnetic tape cartridge was read or written by the tape drive, the tape drive ejected the magnetic tape cartridge. The automatic loader mechanism retrieved the ejected magnetic tape cartridge, placed it into an ejected magnetic tape cartridge stack and automatically advanced the individual magnetic rack to the next individual magnetic tape cartridge storage slot that contained an unused magnetic tape cartridge.
There were a number of disadvantages with the automatic loader described above. First, it was time consuming for the operator to load the magnetic tape cartridges one at a time into corresponding individual magnetic tape cartridge storage slots in the automatic loader mechanism. Second, the use of individual magnetic tape cartridge storage slots consumed space in the loader mechanism and required additional mechanisms to operate. Finally, the automatic loader was a unidirectional mechanism, in that it could only load magnetic tape cartridges into the tape drive mechanism and eject spent magnetic tape cartridges into the spent magnetic tape cartridge stack. Any magnetic tape cartridge that was placed in the spent magnetic tape cartridge stack could not be reinserted into the tape drive by the automatic loader mechanism.
U.S. Pat. No. 4,835,634 to Ostwald, and assigned to Storage Technology Corporation, herein incorporated by reference, discloses a prior art automatic magnetic tape cartridge stack loader apparatus, shown in FIG. 1 hereof, which addressed these problems. The loader is mounted in front of an associated tape drive for loading and unloading magnetic tape cartridges in the associated tape drive. The automatic magnetic tape cartridge loader apparatus comprises a stack loader slot 100 that enables an operator to load an entire stack of magnetic tape cartridges into the apparatus rather than having to load individual magnetic tape cartridges into individual magnetic tape cartridge slots.
The stack loader slot 100 is supported on the bottom by a drop mechanism 103 that translates the stack of magnetic tape cartridges in a downward direction so that the bottom most magnetic tape cartridge in the stack is in position in front of the access port of the associated tape drive, and supported by a load mechanism 104 for insertion into the associated tape drive.
The stack loader slot 100 is bounded on two sides by stack grab plates 101, 102. These plates 101, 102 are movable in the horizontal direction (illustrated by arrow C) to come into contact with the stack of magnetic tape cartridges loaded in stack loader slot 100 and to securely hold the stack of magnetic tape cartridges in a clamping operation. The stack grab plates 101, 102 operate to clamp the stack of magnetic tape cartridges, less the bottom most one, as the stack is translating downward. Once the bottom most magnetic tape cartridge is positioned on the load mechanism 104, the drop mechanism 103 is operated to be repositioned under the remaining stack of magnetic tape cartridges held by the stack grab plates.
A tractor mechanism 126 is then activated to load the magnetic tape cartridge from the load mechanism 104 into the associated tape drive. When the magnetic tape cartridge is ejected from the associated tape drive, the tractor mechanism 126 loads the ejected magnetic tape cartridge onto the load mechanism 104 where it is placed on to an elevator mechanism 112 that supports a stack of ejected magnetic tape cartridges.
There are a number of disadvantages to the automatic magnetic tape cartridge stack loader apparatus. The pressure placed upon the magnetic tape cartridges in the stack during clamping operation by the stack grab plates 101, 102 may deform or distort the magnetic tape cartridge, thereby running the risk of rendering it unreadable/unwritable by a tape drive. In addition, the stack loader apparatus does not provide the functionality to randomly access for subsequent reloading onto a tape drive for reading/writing any magnetic tape cartridge at any time. Finally, gravity is essential to the proper operation of the drop mechanism in stack loader apparatus. Therefore, the stack of magnetic tape cartridges must be aligned along a vertical axis for the stack loader apparatus to operate properly.
For the foregoing reasons, there is a need for an apparatus that (1) individually removes magnetic tape cartridges from a stack of magnetic tape cartridges without causing the deformation or distortion thereof, (2) can randomly access any object in the stack, and (3) can operate upon a stack of magnetic tape cartridges aligned along any axis.